一种改进的星图降噪算法研究

在星敏感器的使用过程中，由于外界环境的影响及传感器自身的限制，拍摄出来的星图不可避免地存在一些噪声，因此对星图进行去噪处理是一项非常重要的工作。针对传统高斯模板滤波存在的引入邻域噪声、无法自行根据星图特性修正等造成去噪效果不好的问题，提出了一种改进的星图降噪算法。该方法在滤波前先进行坏点剔除工作，并采用高斯低通滤波与高通滤波结合的方式对图像进行处理，在抑制噪声的同时有效地保留了星点信号。通过阐述星敏感器的工作原理，分析星图的噪声特性，对星图滤波去噪算法进行研究，并进行模拟星图影像提取星点坐标实验。结果表明：使用该算法进行滤波比传统的高斯滤波算法提取的质心坐标精确度更高，较传统方法横坐标提高0.00538个像素点，纵坐标提高0.0077个像素点，证实了图像处理算法的有效性。     

Wolf-Rayet stars in starbursts

Let us suppose that it is possible observationally to determine the number ratio of WR to O stars in a starburst galaxy (cf. e. g. Vacca &; Conti 1992) and that one can also have some information on the way the different WR subtypes are distributed (number ratios as WN/WR, WNL/WR etc ...), the question is, what can we deduce from these values on the burst of star formation which gave birth to these WR stars? Is it possible for instance to constrain the age of the burst (i.e. the time elapsed since the beginning of the burst of star formation), its intensity (i.e. the ratio of the star formation rate during the burst to that before the burst) or the metallicity of the cloud from which the stars formed? We present here models of starbursts based on the most recent models for single stars computed by the Geneva group and show that the study of the WR population in a starburst provides very useful insights on the age of the burst and on the metallicity of the star forming zone.     

一种改进的三角形星图识别方法

首先提出在直角坐标系下将天球球面均匀地分成486个分区的方法——"内接正方体法",实现导航星的快速检索。然后按照星对角距的大小升序排列,直接存储星对角距,并通过设置星对角距状态标识,完成星对角距的快速匹配搜索。最后,引入验证识别环节有效地解决观测三角形与匹配的导航三角形产生的冗余问题。仿真实验表明,改进的三角形星图识别方法对星点位置噪声和星等(亮度)噪声均具有较强的抗干扰能力,且在识别时间和存储空间的需求方面均比传统的三角形算法也具有较大的优势。     

阵风/叶栅干涉噪声的一种前馈控制策略研究

 基于反问题的研究思路,探讨了阵风/ 叶栅干涉噪声的一种前馈式主动控制策略。具体研究思路是试图通过在静子叶栅表面引入附加的“二次级声源”,精确地消去所感兴趣区域的声音,二次级声源强度基于阵风/ 叶栅干涉气动声学反问题模型获得,并通过数值实验的方法探寻了二次级声源合理布放策略。研究结果不仅证实了在叶栅表面布放偶极子声源的可行性,而且提出了在尽量不影响气动性能前提下的前馈主动噪声控制方法。     

内燃机声强测试的有效性研究

有普通内燃机试验间内用声强法对发动机噪声进行测量,重点依据ＩＳＯ９６１４－Ｉ国际标准对测试数据的有效性和精度进行较深入的分析和校核,结果表明其方法可行,数据有效。通过测量分析,估算了发动机辐射的声功率及声能分布,进行了内燃机声源识别,获得了该型发动机噪声的有关特征和规律。此项研究为在普遍试验间进行内燃机噪声测量分析提供了经验。     

Two-dimensional radiation-hydrodynamics calculations of the formation of O-B associations in dense molecular clouds

Two-dimensional calculations of ionization-shockwave propagation into a curved molecular cloud are presented. Density enhancement occurs due to the combined effects of cloud curvature and radiation flow. The star formation process is expected to be enhanced near the edges of irregularly shaped molecular clouds.Authors listed alphabetically     

The Estimation of the "Center of Gravity" of a Photon Density Profile in Noise

A model for an optical position estimation system is developed employing the photon Poisson process theory. The position estimate is based upon the definition of a center of gravity (CG) of the power density profile of the optical source on the focal plane. An estimator structure is derived using maximum likelihood estimates of the image profile. The resulting estimate of the CG is shown to be unbiased and its variance is obtained. The variance is shown to depend upon the signal energy and noise level as well as upon the distance of the center from the initial counting point. Thus, a composite estimation system is presented which reduces the variance and yet yields a simple structure. Studies on star estimation have yielded position accuracies better than 0.1 seconds of arc for a 2.5 visual magnitude star in a background of equivalent intensity.     

AD－200轻型飞机舱内噪声源传声途径识别

为使建立在双传声器互谱声强基础上的识别方法在飞机上应用,进行了模拟测量。分别以带号筒的扬声器和激振器模拟空气传声和结构传声。模拟测量结果表明：空气传声和结构传声平均声强级识别值的误差分别为１．７ｄＢ（Ａ）和０．４ｄＢ（Ａ）,满足工程应用要求。在此基础上,对ＡＤ－２００轻型飞机在发动机工作下进行了地面测量。结果表明机舱内噪声主要来自座舱后隔板的空气传声。     

国内主流机型客舱声品质表现分析

舱内声环境是决定飞机乘坐舒适性的主要因素之一,而声品质是声环境的一个重要特征。目前声品质分析通常采用主观评价和客观评价两种途径,其中声品质客观评价通过分析噪声数据的频谱特性等物理参数,能更客观的反映声音特性。本文通过高精度的双耳采集设备实测了国内主流机型在巡航阶段的声环境数据,并对相关数据进行声品质客观分析。根据本文测量结果的分析,飞机客舱内的A声级在69.4 dB（A）~83.9 dB（A）之间,响度在28.4 sone~52.5 sone之间,尖锐度分布较均匀,数值在1.1 acum~1.4 acum之间。根据频谱云图结果,噪声源主要集中在200 Hz~400 Hz频段,并且噪声强度在客舱中后部有明显增强。总体来说,各个采样机型客舱内的声品质表现整体处于可接受的水平,其中客舱前部的声品质表现要优于客舱中后部位置。     

CABIN NOISE SOURCE-PATH IDENTIFICATIONFOR AD-200 ULTRALIGHT AIRCRAFT

ＣＡＢＩＮＮＯＩＳＥＳＯＵＲＣＥ－ＰＡＴＨＩＤＥＮＴＩＦＩＣＡＴＩＯＮＦＯＲＡＤ－２００ＵＬＴＲＡＬＩＧＨＴＡＩＲＣＲＡＦＴＹｉｎＪｉａｎｐｉｎｇ；ＨｕＺｈａｎｇｗｅｉ；ＺｈａｎｇＱｉａｎｇ（ＤｅｐａｒｔｍｅｎｔｏｆＡｅｒｏｄｙｎａｍｉｃｓ，Ｎａｎｊ...     

涡喷发动机台架试验声强测量技术研究

本文结合某型涡喷发动机台架试验进行声强测量实践,重点研究了在常规试车台上噪声测量方法及实施方案,依据ＩＳＯ９６１４－Ｉ标准对测试数据的有效性及误差等指标进行了考核。对发动机侧面声功率辐射作出估算,进行声源识别并讨论了该型发动机的噪声级,主要噪声源及其特征,结果表明：在常规试车台上进行发动机声强测量其方法是可行的,数据是有效的,为在常规试车台开展发动机噪声测试研究提供了经验。     

Modified Grid Algorithm for Noisy All-Sky Autonomous Star Identification

Grid algorithm is a classical algorithm for all-sky autonomous star identification. However its recognition rate decreases rapidly when the position and magnitude noise increases in the star image. In order to overcome this problem, a modified grid algorithm called the "elastic gray grid algorithm" is proposed. Gray pattern and elastic template matching are introduced into the grid algorithm to enhance its ability to tolerate the position and magnitude noise. Experimental results show that the modified grid algorithm performs better compared with the original one. The elastic gray grid algorithm reached up to a 100% recognition rate under random positional noise in our test bed. Furthermore it increases the original recognition rate from 69.86% to 97%, under the same condition, for both the position and the magnitude noise.     

Precession–nutation correction for star tracker attitude measurement of STECE satellite

Space Technology Experiment and Climate Exploration(STECE) is a small satellite mission of China for space technology experiment and climate exploration. A new test star tracker and one ASTRO 10 star tracker have been loaded on the STECE satellite to test the new star tracker's measurement performance. However,there is no autonomous precession–nutation correction function for the test star tracker,which causes an apparent periodic deflection in the inter-boresight angle between the two star trackers with respect to each other of up to ±500 arcsec,so the precession and nutation effect needs to be considered while assessing the test star tracker. This paper researches on the precession–nutation correction for the test star tracker's attitude measurement and presents a precession–nutation correction method based on attitude quaternion data. The periodic deflection of the inter-boresight angle between the two star trackers has been greatly eliminated after the precession and nutation of the test star tracker's attitude data have been corrected by the proposed method and the validity of the proposed algorithm has been demonstrated. The in-flight accuracy of the test star tracker has been assessed like attitude noise and low-frequency errors after the precession–nutation correction.     

高超声速飞行器组合导航鲁棒滤波算法

高超声速飞行器由于其飞行环境的影响,使得GPS和星敏感器的量测噪声表现出非高斯特性。针对常规基于Kalman滤波的组合导航在非高斯噪声下性能下降的问题,提出了基于鲁棒滤波的高超声速飞行器组合导航算法。方法在惯性／GPS／＆异步量测建模的基础上,通过随机去耦将量测更新转化为线性回归问题,并基于M估计获得状态量最优估计。仿真结果表明,方法对非高斯噪声具有更好的鲁棒性,有效提高了高超声速飞行器组合导航系统的性能。     

EXOSAT observations of active stellar coronae in the Cygnus Loop,T Tau & NGC 2264 regions

A highly variable point X-ray source, first seen by the Einstein IPC, has been positioned with the EXOSAT CMA and identified with a bright (V = 8.5) K0 star. Although in the direction of the southern half of the Cygnus Loop, this star is almost certainly a foreground object and typical of other active cool stars that are related to RS CVn systems.An EXOSAT program to study T Tauri stars failed to detect T Tau itself. However, a strong X-ray source was observed 15 from T Tau, which in its turn had not been seen by Einstein. This new source has been identified with a hitherto unstudied 13 mag star which is likely to be a dMe flare star.The young star cluster NGC 2264 was observed with the EXOSAT CMA in an attempt to identify the sources found during an Einstein IPC study of S Mon. Apart from S Mon itself, only UV-bright objects were seen, but several of these are considered likely counterparts of the Einstein sources.     

8. The thermal balance of the atmosphere of venus

Current knowledge of the temperature structure of the atmosphere of Venus is briefly summarized. The principal features to be explained are the high surface temperature, the small horizontal temperature contrasts near the cloud tops in the presence of strong apparent motions, and the low value of the exospheric temperature. In order to understand the role of radiative and dynamical processes in maintaining the thermal balance of the atmosphere, a great deal of additional data on the global temperature structure, solar and thermal radiation fields, structure and optical properties of the clouds, and circulation of the atmosphere are needed. The ability of the Pioneer Venus Orbiter and Multiprobe Missions to provide these data is indicated.     

核磁共振陀螺信号仿真及噪声分析

核磁共振陀螺具有体积小、精度高、功耗低等优势,有望成为下一代惯性导航系统的核心部件,目前正受到人们的广泛关注。比较全面的介绍了核磁共振陀螺的基本理论,在此基础上利用时间离散化方法推导并建立了能够充分考虑核磁共振陀螺系统动态特性的仿真模型。利用该模型研究分析了锁相环相位、磁场、温度以及探测光强在1×10-5均方根幅度下均匀白噪声对陀螺信号的影响,发现它们对角随机游走、零偏不稳定性影响依次减小,且都具有自身独特的频率响应特性。其中,锁相环相位噪声引起的角随机游走与零偏不稳定性分别为5.1985×102(°)/h1/2、3.4593×103(°)/h,而探测光强噪声引起的角随机游走与零偏不稳定性分别为3.1623×10-1(°)/h1/2、4.7603×10-1(°)/h。该研究对深入分析核磁共振陀螺动力学机理、寻找主要噪声来源、提高陀螺性能具有重要意义。     

民用飞机增升装置气动噪声学风洞试验初步研究

采用模拟退火法阵列优化设计技术设计了对数螺旋麦克风阵列,开发了基于“波束成型理论冶的阵列试验数据处理软件。将风洞麦克风相阵列噪声识别技术用于SCCH模型增升装置气动噪声研究,开展了增升装置气动噪声源的远场定位探测和强度测量,并用数据处理软件对风洞试验数据进行处理。试验结果表明,随着观察频率的变化缝翼噪声声源的位置与强度会发生变化,襟翼侧缘噪声是一个宽频噪声,不同频率下其强度分布存在差异。同时也发现缝翼安装支架对缝翼和襟翼气动噪声声源有较大影响。文中也给出了多种工况下缝翼和襟翼噪声源分布。     

Detection of iron lines in the persistent emission of some X-ray burst sources observed by EXOSAT

We have observed the X-ray burst sources 4U1728-33 and 4U1813-14 with the ME detectors aboard EXOSAT, and present here results of a spectral analysis of their persistent emissions. For both sources the data can be well fitted by a double blackbody continuum and a Gaussian emission line. The two spectral components can be interpreted in terms of a blackbody radiation from the neutron star, and emission from the inner part of an accretion disc. The line feature is consistent with the 6.7 keV iron emission line expected in the presence of a hot extended object (X-ray corona) around the neutron star.     

Star recognition algorithm for APS star tracker: oriented triangles

An efficient star pattern recognition algorithm is presented. The purpose of this algorithm is to make sure of the compatibility of the software and the imaging sensor noise level. The new CMOS APS sensors have not currently reached the same accuracy as the former CCD sensors in position as well as in magnitude determination, especially in the dynamic stages. This algorithm allows the system to recognize the star pattern 20% faster than with reference algorithms. No false recognition has been noticed. Used databases have a size 5 to 10 times smaller, depending on other reference algorithms. Oriented triangles are used to compare the measured star pattern with the catalogue stars. The triangle's characterization criteria propose several solutions in a first time. A unique solution is selected by means of identification and validation methods in a second time. First results, presented hereinafter, are very encouraging, and this algorithm may be used in the future APS star trackers. APS star tracker robustness is significantly enhanced by this method during the critical navigation phases